# Drag co-efficient

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 August 22, 2008, 15:20 Drag co-efficient #1 kamal Guest   Posts: n/a Hi! I am new in the fluent.my task is to find Drag co efficient for the flow over the sphere in the pipe for differnt reynolds number 250 to 1000.sphere is in the center of the pipe and inlet condition of the pipe can be neglected and flow is fully devloped.i did modelling in the gambit for this problem.my pipe diameter is 0.2 m , length is 6 m and sphere diameter is 0 .035m.i specify velocity inlet as boundry condition.Can anyone help me how to specify reynolds number in the fluent.i calculate velocity of the water based on the reynolds number but it is almost zero. Can anyone help me how to find Drag-coefficient for this problem ? Regards, Kamal

 August 23, 2008, 03:36 Re: Drag co-efficient #2 Smith_K Guest   Posts: n/a You cannot input Reynolds number directly into Fluent tool. You know viscosity of the fluid, density and inlet diameter using which you can find the inlet velocity for a particular Reynolds number. Input the velocity as the boundary condition. You custom field functions to calculate the coefficient of drag.

 August 23, 2008, 05:06 Re: Drag co-efficient #3 ashish Guest   Posts: n/a i think if you keep periodic boundary condition in gambit(where we select wall etc.) fluent will ask you mass flow rate, pressure drop by this you can set a desired Re no one has already suggested the other way do reply here so that we can learn as giving advice is easy !!

 August 23, 2008, 12:50 Re: Drag co-efficient #4 kamal Guest   Posts: n/a Thank you very much smith. I cannot understand what is custon field function to calculate Drag co efficient? i am new in fluent.i have one more question.for Finding reynolds number,do i need to specify the diameter of the pipe or diameter of the sphere and how can i find the stagnation angle?can you help me for that plz?? Thank you very much again.

 August 23, 2008, 12:52 Re: Drag co-efficient #5 kamal Guest   Posts: n/a thanks ashish! but i think in the fluent we can't directly specify the reynolds number.and can we give another boundry conditon other that velocity inlet for this problem??

 August 28, 2008, 11:16 Re: Drag co-efficient #6 ashish Guest   Posts: n/a if you keep the periodic condition in gambit fluent will ask for the mass flow rate you can convert Re no interpreting the velocity in terms of mass flow rate give as an initial condition

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